RE: AD conversions

[Keith Doxey <keith.doxey@xxxxxxx>]

Hi Ray,

You need to allow upto 15 volts as a car with a fully charged battery will
be about 14.4 volts.

Simply add a voltage divider to tap of the required voltage. Your source
signal is 0-15v you need 0-5v for the converter so you need to reduce it to
a third of what it was.

dodgy calculations follow as they are affected by the source impedance of
the driving signal and the input impedance of the A/D converter but in most
cases....source impeadance will be low, A/D input impedance will be high so
can be fairly safely ignored.

Simplest voltage divider is 3 x 1kohm resistors in series. Connect one end
to source and the other end to ground. Connect the A/D converter to the
junction of the 2 lower resistors in the chain i.e. the grounded end. That
will give you a 0-5v range. If you get the wrong one you will get 0-10v.

HTH

Keith

> -----Original Message-----
> From: REB.Barnett@xxxxxxx
> [mailto:REB.Barnett@xxxxxxx]
> Sent: 03 July 2000 13:33
> To: ukha_d@xxxxxxx
> Subject: [ukha_d] AD conversions
>
>
> A slightly off topic question, but an answer or pointer to a more
> appropriate forum would be appreciated!
>
> I've now worked out the required bits to add a data logger to my car.
> However, the AD converter accepts an input between 0 and 5v,
> whereas some of
> the outputs I want to capture run up to 12v. How do I
> increase the range of
> the AD converter? Can I simply whack a resistor in line with
> the input, or
> should I do something more sophisticated with an opamp or
> other gadget?
>
> Cheers,
>
> Ray Barnett
>
>
>
>
>
>
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